New federal actions to clean the air should also help to clean up the Chesapeake, although environmentalists and health advocates say the EPA's new standard for ozone pollution doesn't go far enough.

The EPA in March announced that it would lower the allowable concentration of ozone-commonly known as smog-in the air to no more than 75 parts per billion, compared with the old standard of 80.

EPA Administrator Stephen Johnson called the new limits "the most stringent standards ever," and said they will require 345 counties-out of more than 700 that are monitored-to make air quality improvements because they now have dirtier air than is healthy to breathe.

But the new standard did not go nearly as far as recommended by the EPA's science advisers, which told the agency that limits of 60-70 parts per billion are needed to protect the nation's most vulnerable citizens, especially children, the elderly and people suffering from asthma and other respiratory illnesses.

Johnson's decision was met with sharp criticism from health experts, and some members of Congress accused the EPA chief of ignoring the science. The new standard goes counter to the recommendations of two of the agency's scientific advisory panels-one on air quality and the other on the protection of children.

"Today's decision means millions of Americans will not get the protection that the law requires," said Bernadette Toomey, president of the American Lung Association, which had strongly urged the EPA to follow the advice of the science boards.

Johnson said he took those recommendations into account, but disagreed with the scientists. "In the end it is a judgment. I followed my obligation. I followed the law. I adhered to the science," Johnson said in a conference call with reporters.

The action has implications for the Bay cleanup because emissions of nitrogen oxides from power plants, vehicles and other sources are a major contributor to ozone pollution.

About a third of the nitrogen reaching the Bay originates from air pollution, and two thirds of that stems for NOx emissions, with the rest coming from ammonia releases, mainly from agriculture.

NOx emissions have been trending down, and the new ozone standard should continue that trend, as states will be compelled to devise new plans to control air pollution, although the benefits will be less than if a more strict standard had been adopted.

"This action will help the Bay by reducing nitrogen deposition," said Doug Siglin, a lobbyist for the Chesapeake Bay Foundation. "Unfortunately, the EPA administrator ignored the advice of his own scientific experts and failed to act as aggressively as was called for. We can only hope that the next administration will take air and water pollution in the Chesapeake Bay and elsewhere around the country far more seriously than this one has."

Johnson said that state and local officials have considerable time to meet the requirements-as much as 20 years for those that have the most serious pollution problems. The EPA estimates that by 2020, the number of counties failing to meet the new health standard will drop to about 28.